Solid-state light (SSL) emitting devices, including solid-state light fixtures having light emitting diodes (LEDs) are extremely useful, because they potentially offer lower fabrication costs and long term durability benefits over conventional light fixtures, such as those that utilize incandescent and fluorescent lamps. Due to their long operation (burn) time and low power consumption, solid-state light emitting devices frequently provide a functional cost benefit, even when their initial cost is greater than that of conventional lamps. Because large scale semiconductor manufacturing techniques may be used, many solid-state light fixtures may be produced at extremely low cost.
In addition to applications such as indicator lights on home and consumer appliances, audio visual equipment, telecommunication devices and automotive instrument markings, LEDs have found considerable application in indoor and outdoor informational displays. For example, LEDs may be incorporated into overhead or wall-mounted lighting fixtures, and may be designed for aesthetic appeal.
With the development of efficient LEDs that emit blue or ultraviolet (UV) light, it has become feasible to produce LEDs that generate white light through wavelength conversion of a portion of the primary emission of the LED to longer wavelengths. Conversion of primary emissions of the LED to longer wavelengths is commonly referred to as down-conversion of the primary emission. This system for producing white light by combining an unconverted portion of the primary emission with the light of longer wavelength is well known in the art. Other options to create white light with LEDs include mixing two or more colored LEDs in different proportions. For example, it is well known in the art that mixing red, green and blue (RGB) LEDs produces white light. Similarly, mixing RBG and amber (RGBA) LEDs, or RGB and white (RGBW) LEDs, are known to produce white light.
Recent studies have determined that the heat generated from LEDs decreases overall light emission and bulb durability. More particularly, the LED device becomes less efficient when heated to a temperature greater than 100° C., resulting in a declining return in the visible spectrum. Extended operation, and the resulting exposure to high heat, also reduces the effective life of the LEDs. Additionally, the intrinsic wavelength-conversion efficiency for some down conversion phosphors also drops dramatically as the temperature increases above approximately 90° C. threshold.
The amount of light emission directed into the particular environment may be increased by the use of reflective surfaces, which is also well known in the art. Reflective surfaces have been used to direct light from the LED to the wavelength-conversion material and/or to reflect down converted light which is generated from the wavelength-conversion material. Even with these improvements, the current state of the art LED technology is inefficient in the visible spectrum. The light output for a single LED is below that of traditional light fixtures such as those which utilize incandescent lamps, which are approximately 10 percent efficient in the visible spectrum. To achieve comparable light output power density to current light fixture technology utilizing incandescent lamps, an LED device often requires a larger LED or a design having multiple LEDs. However, designs incorporating a larger LED or multiple LEDs have been found to present their own challenges, such as heat generation and energy utilization.